Supplying Reliable Power to Off-grid Industrial Sites

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By Del Williams

Hybrid solar and wind power solutions are enhancing the reliability of power for off-grid, industrial systems. When considering off-grid, renewable energy sources to power sensors, meters, pumps, controllers and communication links at remote industrial sites, the options typically come down to two: solar or wind.

Solar, an inexpensive option, is often selected. With the availability and decreasing cost of small, off-grid wind turbines that operate in even modest wind conditions, however, the better answer is now both.

To enhance power reliability and build in redundancy, many off-grid industrial substations are now being retrofitted with small, off-grid wind turbines.

Hybrid systems that incorporate both solar panels and wind turbines form a complementary relationship with each, compensating for the weaknesses of the other system. Where solar is best during the daytime, wind power works throughout the night. Where solar is better through the summer months, wind power is better in winter months. And, on stormy and overcast days, wind power is the only option for generating power.

Maintaining continuous, reliable power at remote, off-grid substations is a critical concern in industries ranging from oil and gas to telecom, and mining to railroad. If power is lost, key measurement and monitoring equipment along with data communications can lead to production shutdowns, costing tens of thousands of dollars per hour in some cases.

"An unplanned power outage can cost tens of thousands of dollars in lost production and unscheduled downtime," said Tony Kaspari, an electrical engineer at Beabout Co., which consults with industrial companies such as electric, oil and gas, and water-wastewater utilities in the Rocky Mountain area.

"Without continuous remote data, oil and gas producers, for example, might have to shut down production to ensure safety," Kaspari said. "Integrating a $1,000 wind turbine with a new or existing solar power system can ensure that production stays online even during adverse weather conditions."

While the power demands at some of these off-grid industrial sites and substations may not be large, connecting them to the grid is cost prohibitive.

"Since it can cost anywhere from $80,000 to $100,000 per mile to run power poles or lay underground power cables to a remote site, it doesn't make sense to run power for small power requirements," said Brent Busenlehner, president of ReadyFlo Systems, a Corpus Christi, Texas-based system integrator of remote power systems, automated control systems and integrated measurement/production equipment.

Solar power, though relatively inexpensive, is not always as reliable as advertised when paired with batteries for power storage. To generate power, solar panels must collect sunshine at sufficient intensity and at the right angle. This does not occur at night, when it is cloudy, overcast and throughout much of the winter. If snow covers the panels, power is not generated until the snow melts or the solar panels are cleaned off.

"Remote power systems need to be designed for the worst case scenario, which is typically in the dead of winter," Busenlehner said. "In winter, there is only an average of 4 - 4.5 hours of sun per day in South Texas and only three hours of sun per day in the Dakotas, according to the Department of Energy. In the worst case, there is no sun for potentially long periods of time."

Wind power complements solar power because it often produces the most power when solar power is reduced or unavailable, such as at night, in inclement weather and during winter. Wind often blows during long winter nights and is, on average, actually stronger in inclement weather. During winter, average wind speed is highest, as is air density, both factors that contribute to wind generating more power when solar power tends to be least available.

Maintaining continuous, reliable power at remote, off-grid substations is a critical concern in industries ranging from oil and gas to telecom, and mining to railroad. Hybrid systems that incorporate both solar panels and wind turbines are quickly becoming the solution.

To enhance power reliability and build in redundancy, many off-grid industrial substations are now being retrofitted with small, off-grid wind turbines from suppliers such as Primus Wind Power.

Available in several models for areas with different wind speeds and climates, the company's turbines are designed to generate power at wind speeds as low as 6 mph and can generate as much as 40 to 80 kWh a month per turbine, depending on conditions. Each turbine measures about four feet in diameter, weighs about 13 pounds, and costs about $1,000 per unit.

A single wind turbine is able to power several devices. If more power is required, several turbines can be combined together.

Far from a new concept, small off-grid turbines have already been installed worldwide with more than 150,000 units currently operating in the field.

Wind power complements solar power because it often produces the most power precisely when solar power is reduced or unavailable, such as at night, in inclement weather and during winter.

Another benefit of adding wind power to a solar powered system is that it lengthens battery life by reducing the depth and frequency of discharge. Because off-grid industrial devices or substations are powered by wind when solar power is unavailable, this avoids drawing down the system's batteries and significantly increases battery life.

"Adding wind power to a solar system could potentially double battery life because the batteries won't discharge as deeply," Busenlehner said. "Extending battery life reduces system maintenance and replacement costs, and the savings can be significant.

"It is relatively easy to retrofit a remote, off-grid site powered by solar only. With Primus Wind turbines, it's as simple as wiring the leads from the turbine to the batteries and adding some fuses, switches and amp meters for equipment protection. It's even easier to integrate solar and wind power into a brand new system."

AEP’s Service Disconnect Adapter disconnects customer load but maintains power to the electronic meter. The meter maintains reading and communications links for AMR/AMI operations while only disabling the load side.